Ralstonia solanacearum  (Smith, 1896)  Yabuuchi et al., 1996

Bacterial wilt

General

• Bacteria Telluric present mainly in tropical, semi-tropical and warm temperate regions, is severely rife in many countries of Asia (China, Japan, Malaysia, Philippines, Pakistan, Thailand, Vietnam, India), America (States United, Mexico, Brazil, Argentina) and Africa (both north and south). It is now installed in Europe.
• Very polyphagous, capable of infecting many plants, more than 250 plant species belonging to at least 50 botanical families.
• Several strains are known which make it possible to envisage the existence of a complex of species belonging to 4 phylotypes of different geographical origins.
• Observed in the open field as well as under shelters.
• Organs attacked  : leaves, vessels
•  Symptoms :
  • Symptoms present on young seedlings as well as on adult plants.
  • Rapid wilting of young leaves  at the hottest times of the day, often reversible during the night at first (figure 1); they come on suddenly and become permanent. Leaflets and leaves eventually dry out like whole plants at term (Figure of 2).
  • Sometimes sectorial yellowing of the leaf blade which necroses rapidly (Figure 3).
  • Yellowish to brown more or less dark coloration of the vessels observable in the roots, the taproot and the stem (figure 4). The marrow and cortex may show moist, brown lesions.
• >>> More pictures
• Signs  : Perform a "glass of water test" to reveal the presence of bacteria in the vessels. To do this, take a fragment of a stem from the lower levels of the stem, immerse it in a glass of water,: white mucous swirls made up of billions of bacteria appear within 5 minutes (figure 5).

Biology

• Conservation : maintains itself in the soil in a saprophytic state on organic matter for several years up to a depth of 30 cm, and in irrigation water from canals (Holland), rivers (Scotland), ponds or various water reserves. Infects and multiplies on various cultivated plants (sunflower, peanut, tobacco, pepper, cassava, potato, banana) or weeds ( Amaranthus spinosus, Chenopodium album, Cyperus rotundus, Erechtites valerianaefolia, Euphorbia hirta, Hydrocotyle ranunculoides, Malva sp., Physalis minima, Polygonum pensylvanicum, Rumex dentatus, Solanum nigrum, S. dulcamara, Vicia sp., Etc.) not always expressing wilting.
• Infection : penetrates the roots either at the point of emergence of the lateral secondary roots, or through various wounds caused by tools, bites and alterations caused by root-knot nematodes, insect bites, etc.
• Development - Dissemination : once in the cortex, the bacterium quickly accesses the vessels it invades by multiplying; found in the xylem and in the final phase in the phloem. Dispersed in the soil by gaining the roots of neighboring plants, but also through runoff water, contaminated plants and tillage tools, workers during disbudding and leaf stripping.
• Favorable conditions :
  • Appreciates tropical temperatures, between 25 and 35 ° C, humid and heavy soils, with moderate pH,
  • The contribution of a strongly nitrogenous fertilizer would help to sensitize the plants,
  • Parasitism favored by root-knot nematode attacks.

Protection

• Set up nurseries in plots that have not grown sensitive crops. Preferably produce the plants in mini clods above ground, with a healthy substrate. The plants purchased must have been produced under conditions that avoid any risk of contamination.
• No method of protection can effectively control Ralstonia solanacearum during cultivation.
• Carry out crop rotations, even if this measure is not always easy to manage given its large number of potential hosts. Sugar cane, two years of Digitaria meadow, sorghum in green manure, etc. make it possible to sanitize the soil to a greater or lesser extent.
• Consider incorporating plants that are not very sensitive or even resistant (fescue, cotton, soybeans, grasses, corn, rice, etc.) into the rotation.
• Soil disinfection does not seem to be very effective, regardless of the technical option chosen.
• Plant preferably in disease-free plots.
• Use rootstocks and / or resistant varieties.
• Favor the  drainage of the plots and avoid excess soil moisture and monitor the sanitary quality of the water.
• Provide balanced manure, without excess nitrogen, and destroy weeds.
• Avoid root injuries and water stress.
• Work the infested plots last and disinfect equipment, tillage machinery and workers' shoes.
• Eliminate and destroy the root systems and stems of plants at the end of cultivation.